1. Field of the Invention
This invention relates to programmable delay circuits and operating methods with correction for delay time errors resulting from variations in environmental factors such as temperature and power supply voltage.
2. Description of the Related Art
Programmable delay circuits (PDCs) are commonly employed in applications such as timing interpolators, which require delays that can be adjusted under user control. However, because of signal conditioning required to place the timing reference signal in an appropriate state for the variable delay element, and also to condition the timing reference signal to properly drive outside circuitry, an offset time is introduced into the delay circuit. This offset time varies significantly with changes in environmental factors such as temperature and power supply voltage, and thus adds an error term to the desired delay period. This problem is particularly serious for electronic test equipment, which requires a very low temperature sensitivity.
The general approach to reducing delay offset variations has been to try to design circuit elements with minimum temperature sensitivity. Unfortunately, this can add significantly to both the cost and complexity of the circuit, and does not fully resolve the problem.